Crude process fluid extracted from a well is initially separated into a crude natural gas stream and one or more liquid streams. The crude natural gas stream will usually contain acid compounds such as carbon dioxide and hydrogen sulphide as well as being saturated with water. The acid compounds can together with condensed water form liquid acid during handling and transport which may result in corrosion unless all equipment is made of high quality and high cost steel. Further, the presence of water in the natural gas can during temperature and pressure changes result in the formation of solid hydrates that may result in blockage of the passages through the equipment.
The exploitation of subsea wells has gone through considerable developments since the start of the offshore era. The location of the wells has changed both with respect to sea depth as well as distance to shore. This has resulted in new systems for handling the well streams. One such system includes a subsea installation near the wellhead combined with a topside platform, which can be a floating processing platform. Transportation of the well products can take place either through subsea pipelines or via tanker transport. Due to the limited space on a floating platform, generally the amount of process equipment needs to be adjusted to the available. space. One offshore processing method includes letting a major part of the hydrocarbon gas handling take place sub-sea but handling some regeneration processes and side streams topside.
The well fluid from a subsea well will normally naturally have sufficient pressure to proceed from the subsea well head and up to a topside arranged installation.
However, the subsea processing steps will often result in loss of pressure, as the different separation and treatment processes cannot be performed at such high pressures. After treatment the produced stream as well as the treatment solutions employed subsea will no longer have sufficient pressure for transportation to the topside installation. To facilitate transport of the fluids pumps are installed subsea. Power to the pumps is provided from the top side installation. At high sea depths the power demand would be considerable, which requires a considerable power plant on the top side installation and increased dimensions for the power cable and the length thereof.